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Chemical Formula
• Indicates the composition of a compound and the # of atoms in one molecule of an element
• Molecule – smallest particle of a substance that retains the composition and properties of that substance
Two Types of Molecules
• Monatomic Molecule – each molecule consists of a single atom– Ex: Ne, Ar and Ca
Diatomic Molecule – each molecule contains 2 atoms- there are seven diatomic molecules- H2, O2, N2, Cl2, F2, Br2, I2
Major Classes of Compounds
• Ionic Compounds – metal and a nonmetal bonded together
• Molecular Compounds – two or more nonmetals bonded together
Atomic Structure (cont’d)
Atomic Number – Whole number on the periodic table- tells us the number of p+
- tells us the number of e- in the neutral state
Ex: C has _________ p+ and e-
Atomic Structure (cont’d)
Atomic Mass - the average mass of an atom- tells us the number of pt and n0 together
Therefore:# of neutrons = atomic mass – atomic number
Ionic Substances
• 1) A metal combines with a nonmetal
• 2) Electrons are transferred from the metal to the nonmetal
• 3)Elements no longer have a net charge of zero
• 4) Ions – (charged particles) are formed
Ionic Substances
• An element in an uncombined state has equal numbers of protons and electrons.
• Ex: Na 11 p+ Cl 17 p+
11 e- 17 e-
0 charge 0 charge
Lose Electron
• 1) Typically metals
• 2) Atom now has more p+ than e-
• 3) An overall + charge
• 4) “Cation”
Gain Electron
• 1) Typically a nonmetal
• 2) Atom now has more e- than p+
• 3) An overall – charge
• 4) “anion”
Na + Cl NaCl
• 1) each Na atom loses one e-– Na now has 11 p+ and 10 e- net charge
+1
2) each Cl atom gains one e-- Cl now has 17 p+ and 18 e- net charge -1
*** the attraction between the + ion and the – ion is what allows the bond to form
Group #
Element
e- config.
Dot Diagram
# of valence e-
Gain or lose e- ?
How many?
Charge of the ion
1
2
13
14
15
16
17
18
Predicting Formulas of Ionic Compounds
• The total net charge in an Ionic Compound MUST be ZERO
• Ex: Mg and F
Rules for Writing Formulas of Ionic Compounds
1) Write the symbols for the two elementsEx: Cation (Metal) always comes first
2) Determine the charge of each element
3) Determine the subscripts of each elementRemember – the net charge must equal zero
Polyatomic Ions
• Groups of atoms of more than one element that carry a charge– Act as a single ion– Do not usually break up during a
chemical rxn
– Sulfate – SO4 -2
List of Polyatomic Ions
• The sooner you learn them – the better!!!!!
The formula of the ion is placed in parentheses and the subscript is placed outside the parenthesesex: Al +3 and SO4 -2
Al2(SO4)3
Naming Ionic Compounds
Binary Compounds – compounds made up of two elements- name of cation stays the same- name of anion – ending changes to –ide
Ex: NaCl – sodium chloride
Naming Ionic Compounds (cont’d)
Ternary Compounds – compounds made up of three or more elements
- usually include a polyatomic ion - both ion names stay the same
Ex: MgSO4 - magnesium sulfate
** Exception – when NH4 +1 bonds with a single element (ex: NH4 +1 and O) the ending changes to -ide
Stock System
• CuCl2 vs. CuCl
• Both compounds CAN NOT be named Copper Chloride – we need some way of distinguishing between the two
Stock System
• Name of metal is followed by a Roman Numeral which indicates the charge of the cation *** look at previous example
Traditional System
● Uses suffixes at the end of the metals Latin root
● Smaller of the two ions receives suffix of
– ous● Larger of the two ions receives
suffix of -ic
Traditional System
Fe +2 ferrous Pb +2 plumbous
Fe +3 ferric Pb +4 plumbic
Cu +1 cuprous Sn +2 StannousCu +2 cupric Sn +4 Stannic
Formulas of Molecular Compounds
• Molecular Compounds – made up of molecules rather than ions– 2 or more nonmetals bonded through
the sharing of electrons
Oxidation #
• Apparent charge of an atom as it attracts or repels e- from another atom
• Oxygen typically has a -2 oxidation #
Example
N2O nitrogen (II) oxide N = +1
NO nitrogen ( ) oxide N =
N2O3 nitrogen ( ) oxide N =
NO2 nitrogen ( ) oxide N =
N2O5 nitrogen ( ) oxide N =